Electrical signaling system



June 29, 1948. w. H. P. PouLlARr ELECTRICAL SIGNALING SYSTEM 2 sheets-sheet 1 Filed Jan. 16, 1945 INV ENTOR. 4 l//L L YAM' POuL/HRT 5)" ATTOR June 29, 1948. w. H. P. PouLlAR'r ELECTRICAL SIGNALING SYSTEM Filed Jan. 1e, 1943 2 Sheets-Sheet 2 INVENTOK v ff/Ufff POuL/HFT TTUR nomic operation.

Patented June 29, 1948 ELEc'rmcAL SIGNALING SYSTEM Willy H. P. Pouliart, Antwerp. Belgium, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application January 16, 1943, Serial No. 472,614

In the Netherlands April 1941 .Section 1, Public Law 690, August 8, 1946 Patent expires April 15, 1961 19 Claims. (Cl. 177-353) 1 This invention relates to new and useful im provements in an electrical signaling system, and

' particularly to selective signaling arrangements for telephone switching systems and the like.

The signaling system' forming the object of this invention, makes use of apparatus at both ends of a signaling wire or circuit, ,the apparatus at one end` being used-.for registering or receiving certain indications, e. g. a register controller operated in accordance with the called number, and the apparatus at the other (identiiying) end being used for the identiiication of these indications, e. g. a selector set in accordance with the setting of the register controller.

In accordance with the present invention. characteristic, predetermined direct current poten.

tials are connected by the receiving apparatus or register controller to one end of the signaling circuit in accordance with the setting of the receiving apparatus. A similar range of differpriate detector means inserted in the signaling circuit.

For the sake of simplicity, in the following description, we shall assume that apparatus A and- B are switches of the well-known single-motion type used in telecommuniction systems, b being the rotating brush member, and a a row of bank terminals provided for each switch. It should be understood, however, that the inventionis by of about 2 volts between adjacent bank terminals.-

ent characteristic direct current potentials are connected to the other end of the signaling circuit by the apparatus, e. g. selector,I at the identi fying end. An appropriate detector provided in the signaling circuit responds only if the two potentials bear a predetermined relationship to one-another, e. g. 'if a predetermined minimum difference of a predetermined polarity exists between the potentials applied to the two ends of the signaling circuit.

The details of the signaling system may be varied, some variations being described herein by way of example. This novel signaling system oiiers many advantages over other systems used for identification or selection, especially when it is desired to insure reliable, flexible and eco- The principle of operation is diagrammatically illustrated in Fig. 1. Fig. 2 shows the .diagram of a practical embodiment in a telephone system or the like. Fig. 3 shows an application of the invention to a circuit arrangement for remote control.

In Fig. 1 apparatus A designates a rst switch which may be any kind of electrical or mechanical appliance and which can occupy different, independent positions. The drawing shows a switch having a. brush wiping over a bank of terminals, but any combination of relays, contacts on circuit breakers, etc., may be used. Apparatus A is located at one end of a signaling wire or circuit and is arranged for the reception and the registering of any kind of electrical or mechanical indications, which it is desired to transmit to the distant end of the signaling circuit for identification.

A second switch B is like A and may be any kind of electrical or mechanical appliance, ca-` pable of exploring or hunting over a plurality of independent contacts under control of approno means limited to such apparatus.

The individual bank terminals of switch A are so connected that different direct current potentials are applied'thereto. In Fig. 1 the source is, by way of illustration, represented in the form of a battery, of which a tapping from each consecutive cell is connected to consecutive bank terminals. thus creating a diierence of potential It should beunderstood, however, that any other source of D. C, may be used, and that any appropriate difference of potential between adjacent bank terminals may be employed.

The individual bank terminals of switch B are also connected to dierent direct current potentials. For the sake of simplicity, the same source of electromotive force is used forboth switches. Obviously, individual sources can be used for the two switches, provided that at least one common connection exists between the two individual sources. v

The signaling system comprises also a detector arrangement D inserted in the signaling circuit. The purpose of the series rectifier R isl to ensure that the detector is actuatedpnly by a potential determined relationship, e. s.. a predetermined minimum potential-difference of a predetermined sign (plus or minus) exists between the two ends of the signaling circuit.

The detailed manner in which the new signaling system functions will now be explained:l

Assume that the brush bu of switch A, as a consequence of an indication received, has been set in the position shown in Fig. l, resulting in the application of a certain potential to one end of the signaling circut. When so set, switch A will, under the control of suitable means which may include the detector D, close a circuit for the operating magnet M of switch B, which will start to rotate its brushbo over its bank f terminals b, thus connecting varying direct current potentials to the other end of the signaling circuit. When the brush bo of switch B reaches a position in which a potential is applied to its Vend of the circuit and which differs from the potential applied to the other end by a 'predetermined amount 2p, of a predetermined sign, then, with the series rectifler arranged as shown, the detector D will function and open the circuit of the magnet M of switch B, which wi 'stop rotating. The position of switch B, shown in dotted lines in Fig. 1, serves to identify the indication originally received by switch A.

In order to illustrate the practical application of the signaling system according to the invention, its embodiment in telecommunication, e. g. telephonesystem, is shown in Fig. 2. However, only such details are disclosed as are necessary for explaining the invention, vi. e. the circuit components operating during the selection proper,

` from the moment a digit is received in a register controller until the selector switch has been set in accordance with the digit received. f y

A step-by-step rotary switch Sconstitutes the digit receiving apparatus in a register controller.

. Only two banks of contacts a and b with associ-- ated brushes are shown. The terminals of these banks are connected to diierent points of a. potentiometer.A For the sake of simplicity, the connections of only five terminals are shown. l The rst terminal in bank a is connected to the lowest potential, while the following terminals are cony nected to consecutive taps of the potentiometer in the direction of growing potentials. The termanner which depends on the potential difference to which the detector is designed to respond. If the potential diierence between consecutive taps of each potentiometer is designated by p volts, and if it is assumed that the detector is designed to respond to a potential difference of +2p volts, then the rst terminal in bank g, i. e. the terminal identied 4by the digit 1 received by switch S, must be connected to the same potential as terminal 3 of bank a of switch S. The other terminals in bank g are connected to consecutively higher potentials.

The detector shown in Fig. 2 comprises a "co1dcathode tube, a transformer, several rectiers, a

resistance, a potentiometer and a direct current source of l130 volts.

The cold-cathode tube L is of the wen-known type which requires a speclc control gap breaktively. Oneslde of this winding is permanently connected to brush y of switch SM, while the other side is connected to brush a (or brush b) of switch S via contacts of the controlling relays Ar `and Br. The purpose of the rectiers associated with this winding will be explained later. The secondary winding of T is connected in series with control electrode er. The transformer is a step-up transformer so designed that a. sudden application of a difference oi potential of +2p or more between the two ends of the signaling wire, causing a current to flow through the primary wlnding in the direction indicated by an arrow drawn in full lines, will produce an electrical surge in the secondary winding, which creates a potential added to Vp, the sum being sutlicient to break down and to ionize the control gap.

'I'he relays Gr and Gtr form part of the register controller.

The detailed method of operation of the arrangement shown in Fig. 2 is as follows:

When the digit receiving switch S has been set to a position corresponding to a received impulse train, thus .registering a digit, the register controller closes (by means indicated by switch SW not fully disclosed but as described for example in U. S. Patent No. 1,556,474 to A. Barnay) a circuit for the power magnet of switch SM, via the switch magnet and back contacts of the relays Ar, Cr and Gtr to ground. The relay Ar is slow to release. Switch SM starts stepping the magnet acting as its own interrupter, causing brush gto wipe over consecutive terminals in the bank. Every time that brush y encounters a terminal, a certain potential will be applied to one side of the primary of transformer T, the other side of which is connected to the potential determined by the position of switch S.

Assuming that digit 4 has been sent, and that brush a of switch S is on terminal 4, the potential difference between'the two sides of the primary winding of T will vary as follows:

When `brush g reaches terminal I, the potential diierence is 11.

When brush g reaches terminal 2, the potential diil'erence is 0.

When brush g reaches terminal 3, the potential diierence is .+9.

When brush g reaches terminal 4, the potential difference is +29.

When, therefore, terminal t is reached, the potential diierence +2p causes the ionization of the control gap of the cold-cathode tube L, as previously explained. This ionization causes the ionization of the main gap of the tube, resulting in the operation of relay Gtr, which is connected Electrode e2 is connected to the negative side brushes a. and b of switches S and SM, respecin series with the anode A; Relay Gtr opens the circuit of the power magnet of switch SM and stops the selector brush g on terminal 4.

The operation of relay Gtr causes the energization of relay Ar in a. circuit via the right inner back contact of Br to ground at the make contact of Gtr.

Relay Ar in turnopens'the anode circuit of the tube L and, since at this moment the electrical surge in the secondary Winding of T has disappeared, the tube will be extinguished, resulting in the deenergization of relay Gtr.

At this moment, the selection process proper is terminated.

The release of the selector switch is effected in the usual manner -by operating its power magthe circuit of the magnet being closed by the deenergization of the relay Br over an off-normal contact ONC of the selector.

A reference will now be made to some other features of the invention, which have been introduced for the purpose of improving the reliability of the new signaling system.VJ

Since the detector is made to respond to a given potential difference .of a given sign, it will also respond to higher potential differences of the same sign. It is, therefore, desirable to check before proceeding with further selections, whether the terminals on which the selector switch y came to rest, are the correct ones, or whether the switch, for some reason, has been overshootleading to terminal 4 in bank g is broken, switch SM would continue to rotate and would come to rest on terminal 5, where a potential difference of +31 would be applied to the detector, which wouldrespond in the usual manner. The selection should, however, y,not be allowed to proceed because it would result in a wrong connection.

For the purpose of checking whether the position taken up by the selector wipers is the correct one, an extra relay Br and an additional bank b in switch-S are provided.

The operation of this feature is as follows:

Let it first be assumed that selector wiper g has stopped on terminal 4, which would be correct.` After the extinguishing of the tube and the release of relay Gtr, as explained above, relay Ar will remain energized over its own front contact. in series with relay Br. Over the left outer front contacts of Ar and Br the anode A is again connected to relay Gtr, While the primary winding of transformer T is transferred from brush a to brush b of switch S via left inner front contact of Br. The primary winding of T is now sub-V jected to a difference .of potential equal to -l-p, due to the staggering of the terminals of bank b with respect to a. v

The detector will not respond to this difference.

If the wire 4 of SM is broken and the wiper g stops on terminal 5, then after the extinguishing of the tube and the release of Gtr, relays Ar and Br energize in series, and the primary winding of transformer T is subjected to a difference of potential of +2p. The detector will respond to this diiference. in the manner previously explained, resulting in the ionization of the tube and the energization of relay Gtr for the second time. Relay Cr will now operate over front contacts of Br and Gtr, and Cr in turn opens the anode circuit, thus extinguishing the tube. Relay Cr locks over its own front contact and gives an indication to the register controller that `the selection has been erroneous., The' opening of the middle right hand contacts of the relay Cr may be used, for example, to give such an indication.

Another feature which forms part of this invention, will be better understood afterhaving made an analysis of the two conditions on which the satisfactory functioning of the new signaling system primarily depends, viz: l

(a) The operating limits of the cold-cathode tube. v l

(b) The possible variation of potential difference between the two ends of the signaling circuit, i. e. between brush g of switch SM and brush a of switch S.

I. A cold-cathode tube can be ionized in two diderent ways, by a modification of the control electrode potential, viz:`

(a) By increasing the control anode potential with respect to ground, so as to cause the breakdown (ionization) of the control gap. 1

(b) By decreasing the control anode potential with respect to ground, so as to cause theibreakf' down (ionization) of the main gap or of the control gap,

By way of example, the control gap breakdown voltage may be about 'I0 volts, -while the main gap breakdown voltage may be about 175 volts,

II. The maximum potential dierence between brushes a and a depends on the maximum number of indications which it is desired to receive and transmit, in the case under consideration, l

ten different digits Oto 9. On receipt of digit 0 brush a will be moved to terminal ill, and when subsequently brush g arrives on terminal l, there will be a maximum negative difference of potential between brushes y and a of 8p volts.A 'I'he maximum positive difference will normally not exceed +2p volts, because the detector is designed to function on such adiiference.

lThis leads us to an explanation of the purpose of the rectifiers shown in Fig. 2.

Let it be assumed that digit 0 has been received and that brush g has-arrived at terminal l, thus establishing a difference of 8p volts between g and a. The direction of the current flowing through the primary winding of ,transformer T is opposite to that required for the regular operation of the tube, and is indicated by an arrow in dotted lines. This current might be sumcient vto induce an electrical surge in the secondary winding of transformer T of, such a direction and magnitude, that the main gap breakdown voltage would be reached. In order to avoid this, three rectiilers R1, Rz, and Ra have been introduced. l

The rectiers R1 and Re are placed in series with the primary winding of transformer T and are so poled that the operating current of the detector is practically not iniiuenced, while the reverse current is considerably reduced `in magnitude. Due to the leakage current in all commercial rectifiers and also dueto the transient reverse current passing,`owing to the capacity n of the rectiilers, a small reverse current will, nevertheless, pass through the primary winding of transformer T. Even `this small current can be considerably reduced by the introduction of the oppositely poled rectifier Re, which is con.-

nected in shunt to the primary winding of tranlformer T and rectifier R2. R3 offers very small resistance to any reverse current, in comparison with R'z, so that practically all `reverse current through the primary windingI of transformer T is eliminated. A still further safeguard is provided in the rectifier R4, which is poled like Ra and provides a low resistance path for the electrical surges induced in the secondary winding of` direction of the "make" surge.

The break surge is only of importance in aumen cases when high negative potential is applied'to brush g with respect to brush a. This is so because the speciiic "break surge, which may be particularly great in magnitude, has the same direction as the normal operating surge and might provoke the ionization of the control gap. 'Ihis vdanger is eliminated by the rectifier arrangement biasing potential, to the control electrode so as to allow a comparatively small additional potential to cause the ionization of the control gap.

Another application of the invention is shown in Fig. 3, where the remote control of lcircuit breakers is illustrated to the extent necessary for understanding by those skilled in the art.

Each circuit breaker has associated therewith a pair of signaling contacts SC arranged on rack RRI. Each pair of circuit breaker signalling contacts of which in Fig. 3 only pair SCi is shown,

terminates in two terminals SCi in 3. 4 of bank;

al of a selector switch S1, after having passed control circuits (I, 2) arranged on a second rack RRZ and drawn in dotted lines. 'The function of these control circuits is indicated by switches I", Z'. These switches I', Z' are operated in a manner which is not shown and which is considered immaterial for the invention, whenever a change in the position of contact pair SCi occurs.

Thus, a change in the position of one of the circuit.breakers causes the associated signaling contact SC. in Fig. 3, one of the back contacts of SC; to be engaged, the associated switches I", Z' to be closed and circuits I and Z to be connected to terminals 3 and 4 of bank al. As a consequence either 3 or 4 of bank al will be grounded depending on the fact that whether the circuit breaker changed its `position from out to in or, as shown in Fig. 3, from fin to "out. The means causing the closure of switches I', Z' and the connection between contacts SCi and terminals 3, 4 of bank a1 also close switch 3' and control circuit 3 indicated in dotted lines in rack RRZ. Circuit 3 excites magnet S1 which produces a. step-wise rotation of brush aul over the terminals of bank al. As soon as brush ao1 engages the grounded terminals 4 of bank a1, control`circuit Z in rack RRZ is energized over au1 and battery Bo. This causes, by means not shown but well known in the art. switch 3 and control circuit 3 to be opened. This interrupts the energization of switch S1 and causes brush aol to be stopped on the grounded terminal 4 of bank a1. Control circuit 2 also operates other control circuits and switches which are described further below.

In this way a change in the position of one of a number of circuit breakers causes the switch to rotate to the terminal marked by ground, corresponding to the changed position.

The invention is not concerned with the Way in which brush aol is caused to reach a predetermined position. Racks RRI and RRZ, contacts SC. control circuits I, 2, 3, 4 and 5 as well as switches I', Z', 3', 4 and 5 are only symbols explaining the operations to be performed.' These symbols can be replaced by any devicefor selector switch by means of grounding a terminal, hunting for the grounded terminal and stopping the selector switch when the hunting brush reaches the grounded terminal, is well known in the art `oi using selector switches and requires no further description.

Bank b1 of switch Si is wired to a potentiometer P1 and connects a. direct current potential to the signaling wirel 4" leading over control circuit 4 and, switch 4' (shown in/'dotted lines) to detector D which in turn is connected over wire 4"' tothe distant control station.

` When switch S1 has been duly set in position d of bank al control circuit Z not only deenergizes magnet circuit 3, but also, by means similar to those used for the deenergization of circuit 3 and equally well known in the art, switches 4', 3' and control circuits 4, 5 are operated. -Control circuit 4 and switch 4' connect brush bo1` and poten-` tiometer Pi to detector D. Control circuit 5 and switch 5 are grounded in the front contact of relayGtr when the latter is operated by detector D. Thus, an energizing circuit is closed for the power magnet of the distant control switch S2 which starts to rotate under control of a detector D like the one in Fig. 2.

Bank b2 of switch S2 has a brush bc2 connected to detector D, and terminals I, Z of bank I)2 connected to a potentiometer Pz, and connections are such that when the two brushes bei and lm2 are in corresponding positions then a potential difference of +23) volts will exist between brush bo of S2 and brush bol of Si which will cause the detector D to respond.

For checking the correct position of switch S2. a third bank is required on switch Si. This third bank'has not been shown, since its wire and functions are identical with those in Fig. 2.

When the detectorl responds, relay Gtr operates and stops the rotation of switch Se, in exactly the same position of brush lm:i as that of brush bol. The indication on a signal panel SP is given bank a2 of switch S2.

If the circuit breaker at the central station is moved from the-outposition into the in" position, the brushes aol. bol and an, lm2 of switches S1 and Sz will occupy the positions shown in 'dash dotted lines' over terminals 3 of `banks 'al and a2 respectively. In this position of ySn relay Sr at the distant station operates and locks. causing the lamp In to light.

When the circuit breaker falls off again into outposition, switches Si and S2y will occupy the positions shown in dotted lines over terminals 4 of banks b1 and b2, respectively. In this position of S2 relay Sr at the-distant end will then be-short-circuited and unlocked causing i pendent upon the operation of the rst switch,

a source of directcurrent potentials each having a different predetermined magnitude, a connection from said source over the first4 switch to said detector having one of said direct current potentials of predetermined magnitude, said con nection dependent upon the setting of said iirst switch, a connection from said source over the second switch to said detector having one of said direct current potentials of predetermined magnitude, said connection dependent upon the setting of the second switch, means for actuating said detector when it is subjected to two different potentials of predetermined diiference, a relay, and means for actuating said relay when said detector is actuated by a higher potential than said diilerence.

-2. .In an electric signaling system, a i'lrst switch and a second switchmeans for variably operating the first switch, switch controlling means including a detector for variablyoperating the second switch dependent upon the operation of the iirst switch, a source of direct current 'potentials each having a different predetermined magnitude, a connection from said source over the iirst switch 'to said detector having one of said direct current potentials of predetermined magnitude,

,said connection dependent upon the setting of i said first switch, a connection from said source over the second switch to said detector having one of said direct current potentials of predetermined magnitude, said connection dependent upon the -setting of the second switch, means for actuating said detector when it is subjected to a potential difference exceeding a predetermined minimum, a relay for indicating incorrect setting of said second switch, and means for actuating said relay when said detector issubjected to a, potential diierence which exceeds said minimum potential difference by ya predetermined amount.

3. In an' electric signaling system, a first switch having two backs of terminals and a brush cooperating With each bank, a second switch hav- N ing a bank of terminals and a brush cooperating therewith, a magnet for moving the brush of the second switch over its terminals, a signaling circuit extending fromthe brush of th'e second switch and normally connected to a first brush of the rst switch, a detector in said circuit, a source of direct current potential, means for applying to said detector direct current potentials of predetermined magnitudes depending on the position of the brush of the second switch, means for applying to said detector over said first brush of said first switch direct current potentials of predetermined magnitudes depending on the position of said first switch, means for actuating said detector when the difference between the two potentials applied thereto exceeds a predetermined minimum, a first relay, a second relay for Ipotentials of different predetermined magnitudes dependent upon the position of the rst switch, i

means for actuating said detector a second time if the difference between the two potentials applied thereto exceeds a predetermined magnitude and means responsive to the second actuation of said detector for energizing said second relay.

4. In an electric signaling system, a variably operable first switch, a second switch, switch actuating means including a detector for variably operating the second switch dependent upon the operation of the first switch, a source of different direct current potentials each having a predetermined magnitude, a first set of electrical contacts in said first switch and a second set of electrical contacts in said second switch, connections from said source to the respective contacts of the said rst and second sets of contacts, each connection having .one of said diierent direct current potentials, a flrst connection froma nection a single direct current potential of one predetermined magnitude. said Aiirst connection dependent upon the operation of said rst switch, a connection `from a selected `contact of said second set to said detector and means for maintaining along said second connection a single direct current potentialof a predetermined magnitude, said second connection dependent upon the operation of said second switch.' and means for actuating said detector when the two single potentials applied thereto bear a predetermined relationship to one another. i

5. In an electric signaling system, variably operable iirst and second switches, each switch hav- -ing a set of contacts and a brush movable over its associatedset-oi contacts, a magnet for controlling the movement of the brush ofthe second switch over its -associated setV of contacts, a detector for controlling said magnet, a Isource of different direct current potentials each having a predeterminedmagnitude, connections from said source to the respective contacts of each set of contacts and means for maintaining along each connection one of said diilerent direct current potentials, a rst connection from the brush of the contact engaged by the brush of the iirst switch, a second connection to said detector and means for maintaining along said second connection a single direct current potential of one predetermined magnltude, said second connection dependent uponthe position of the brush of the second switch, and means for actuating said detector` when the vtwo single potentials applied thereto bear a predetermined relationship to one another.

6. In an electric signaling system, variably operable first and second switches, each switch having a'set of contacts and a brush movable over its associated set of contacts, a magnet for controlling the movement of the brush of the second switch over its associated set of contacts, a detector comprising a transformer having a primary and a secondary winding and an electron discharge tube having a pair of electrodes forming a control gap and a pair of electrodes forming a main gap, a relay for controlling the operating of said magnet in series with said main gap, connections from the ends of said secondary winding Vto the electrodes forming said control gap, means for simultaneously applying diierent direct current potentials to the respective contacts of each set of contacts, means for applying to one end of said primary winding over the brush of the rst switch a selected direct current potential of a predetermined magnitude depending upon the contact engaged by the brush of the rst switch, means for applying to the other end of said primary winding direct current'potentials of predetermined magnitudes dependent upon the position of the brush of the second switch, and means for applying a xed potential diierence to the electrodes forming said control gap of such value that when the two potentials applied to the said primary winding bear a predetermined relationship said control gap is ionized and initiates the actuation of said relay.

'7. In an electric signaling system, a first switchl l bank of terminals and a brush cooperating therewith, a magnet for moving the brush of the second switch over its terminals, a signaling circuit extending from the brush of the second switch and normally connected to a iirst brush of` the first switch, a detector in said circuit, a source of direct current potential having a row of taps from which potentialsof step-by-step increasing magnitudes may be obtained, connections to successive taps for' the successive terminals cooperating with said brushes, the connections from the terminals cooperating with the second brush of the iirst switch being staggered with respect to the connections to the terminals of the first brush, means for applying to said detector direct current potentials of predetermined magnitudes dependent on the position of the brush of they second switch, means for applying to said detector over said iirst brush of said flrst switch direct current potentials of predetermined magnitudes dependent on the position of said first switch, means for actuating said detector when the difference between the two potentials applied thereto exceeds a predetermined minimum, a first relay, a second relay for indicating incorrect setting of said second switch, means responsive to the actuation of said detector for energizing said iirst relay, means responsive to the energization of said first relayy for transferring said signaling circuit tothe second brush of said first switch, means for applying to said detector over said second brush direct current potentials of different predetermined magnitudes dependent upon the position of the first switch, means for actuating said detector a second time if the diierence between the two potentials applied thereto exceeds a predetermined magnitude, andmeans responsive to the second actuation of said detector for energizing said second relay.

8. An arrangement according to claim 6, further comprising a rectifier connected in series with the primary winding of said transformer.

9. An arrangement according to claim 6, further comprising a'rectiiier poled in one direction connected in series with the primary winding of said transformer and a further rectifier poled in the opposite direction connected in shunt to said primary winding. l

10. An arrangement according to claim 6, further comprising a rectifier connected in shunt to the secondary winding of said transformer.

11. In an electric switching system, a plurality of conductors, means for maintaining along each conductor a predetermined direct current potential, a potential responsive device, means for applying to said device a desired one of predetermined direct current potentials, means controlled by said device for connecting said conductors to said device, and means for operating the device when the potentials applied thereto are different and have a predetermined difference.`

12. In a system according to claim 11, means for connecting said conductors to said device successively, and meanscontrolled by the device for stopping the connecting means.

13. In an electrode switching system, a plurality of conductors, means for maintainingalong each conductor a predetermined direct current for applying, and means for operating the multil2 electrode tube when the potentials applied thereto have a predetermined diilerence.

14. In a switchinglsystem, designated lines, switches each having a bank of terminal sets in which said lines terminate and a set of wipers arranged to wipe over said terminals, a magnet for controlling the movement of the wipers of each-switch, sources of predetermined direct current potentials, connections for placing potentials on lines, one predetermined potential on each line dependent upon its designation, a multielectrode electric discharge device, means for applying to the electrodes of the device potentials eidsting on the terminals of different switches, means for operating said device only when the potentials applied from the switches bear a predetermined relationship to one another, and means actuated upon the operation of the device for controlling one of said magnets to stop the associated wiper. Y

15. The -system according to claim 14, and in which the device is common to said switches.

` `l6. The system according to claim 14, and means for operating one of said switches in accordance with the designations of said lines.

17. In an electric switching system, a plurality of conductors, means for maintaining along each conductor a predetermined steady direct current potential, a device responsive to single potentials of predetermined diiference, means for applying to said device a desired one of predetermined direct current potentials, and means controlled by said device for connecting said conductors to said device so as to operate the device when the potentials applied thereto have a predetermined diierence.

18. In an electric switching system, a plurality of conductors, means for maintaining along each conductor a. predetermined steady direct current REFERENCES CITED The following references are of record in the file of this patent:

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